Tor Browser uses its own instance of the tor daemon and communicates
with it using the Tor control port on 127.0.0.1; the protocol is
documented here:
    https://gitweb.torproject.org/torspec.git/tree/control-spec.txt

tor-launcher is a Firefox extension that uses this protocol to manage
the tor daemon used by Tor browser.  It provides the control and
communications glue used by the torbutton add-on to e.g. display the
nodes in the current circuit, change the tor configuration, etc.
